336 



MORPHOLOGY OF GYMN0SPER:MS 



384 



cell divides into two distinct and unequal male cells, the cytoplasm 

 of the body cell being divided unequally (tig. 386). The behavior 



of the tubes is interesting 

 and suggestive. They may 

 advance rapidly, reaching 

 the female gametophyte at 

 an early free nuclear stage 

 (16-64 nuclei) , or they may 

 advance ^'ery slowly. The 

 course may be very direct, 

 resulting in a straight cleft 

 through the tip of the 

 nucellus, or it may be ex- 

 tremely devious. In one 

 case observed the tube ad- 

 vanced directly half-way 

 through the tip of the 

 nucellus ; then proceeded 

 spirally downward and out- 

 ward to the peripheral cells 

 of the nucellus, several of 

 which it destroyed; then 

 turned abruptly inward, 

 penetrated the nucellus at 

 the level of the arche- 

 gonium, crossed the top 

 of the endosperm, and dis- 

 into the arche- 

 on the opposite 

 side. In another case a 

 wandering tube penetrated 

 the inner integument before 

 turning back into the nu- 

 cellus. Very frequently 



charged 

 gonium 



Figs. 384, 385. — Torreya iaxifolia: fig. 384, 

 tip of nucellus with pollen chamber (disintegrated 

 tip of nucellus) containing a two-celled micro- 

 spore, the smaller cell being the generative cell 

 and the larger the tube cell; pc, pollen chamber; 

 X220; fig. 385, end of pollen tube in contact 

 with embryo sac, which is in free nuclear stage; 

 in the tube the stalk and tube nuclei are in advance 

 of the body cell; X460. — After Coulter and 

 Lakd (ioi). 



the tube pushes into the 



embryo sac at the free nuclear stage, making a deep invagination 



(often to the middle of the sac), and from this pocket it turns back 



